1. Field Of The Invention
This invention relates to a releaseable fastener, and in particular to a slotted fastener having a displaceable retainer sleeve to release the fastener.
2. Brief Statement Of The Prior Art
Releaseable fasteners, typcally separation nuts, have been used in various aerospace applications, often with explosive squibs or with fluid pressure, for remote release. These devices have universally used an axially displaceable retainer which surrounds an assembly of a segmented nut fastener. Many complex designs have been developed with annular cavities in the retainer ring, such as in U.S. Pat. No. 3,334,536 and cams or levers have been provided to impart a positive separation force to the segments as the retainer sleeve is displaced, e.g., see U.S. Pat. No. 3,120,149. The latter patent also discloses a hexagonal interface between the segmented nut and the retainer sleeve to transmit torque. This patent, however, uses two nut segments which precisely mate, without any axial separation slot. The nut segments of this patent would be quite costly to manufacture, as each nut segment must be separately machined.
U.S. Pat. No. 3,813,984 discloses that a practical and cost effective method of manufacturing a segmented nut fastener is by axially slitting a preformed nut fastener. This, however, creates axial separation slots between the segments. In U.S. Pat. No. 3,170,363 the axial slots are filled with plastic fins which provide thread locks. Plastic fins, however, cannot transmit any significant torque, and axial keys are provided between each of the nut segments and the retainer sleeve to transmit the fastening torque. Thus, the most economical method of manufacture of slitting nuts, has heretofore precluded a simple design for transmission of fastening torque, and most designs have used complex keys and mating keyways between the nut segments and the outer, retainer sleeve.
Another undesirable feature of the separation fasteners which have previously been used is the separation shock generated upon the release of the retainer sleeve, which is particularly severe with the explosive-squib-actuated fasteners. Again, complex designs such as disclosed in U.S. Pat. No. 3,813,984 have been developed for minimizing or balancing the mechanical shock of release, but not attempt has been made to change the fundemental nature of the release to eliminate the release shock.